Process for purifying polyhalogenated carboxylic acids



Sept. 15, 1959 Filed Nov. 6, 1957 INVENTOR EDGAR FISCHER United StatesPatent PROCESS FOR PURIFYING POLYHALOGENATED CARBOXYLIC ACIDS EdgarFischer, Frankfurt am Main, Germany, assignor to Farbwerke HoechstAktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt am Main,Germany, a corporation of Germany Application November 6, 1957, SerialNo. 694,870

6 Claims. (Cl. 260-408) This invention provides a process for purifyingcrude polyhalogenated carboxylic acids and more especiallypolyhalogenated carboxylic acids containing fluorine and chlorine.

As starting material for the manufacture of polyhalogenated carboxylicacids there may be used polyhalogenated parafiin mixtures which may beobtained, for example, by the telomerization of polyhalogenated olefinscarried out, for example, according to U.S. Patent 2,770,659 or by thecracking of high molecular Weight perhalogenated polymers or copolymersof halogenated olefins according to the process described in US. patentapplication Serial No. 525,783, filed on August 1, 1955, by EdgarFischer and Hans Helmut Frey for Production of FluorochlorocarboxylicOils and Waxes or according to other suitable processes. By a treatmentwith oxidizing agents the unsaturated constituents contained in themixtures of saturated and unsaturated halogenated paraflins areconverted into the polyhalogenated carboxylic acids. The saponificationof the saturated constituents resulting in their transformation intopolyhalogenated carboxylic acids can only be effected by means of anacid under very energetic conditions, for example, under the conditionsdescribed in US. patent application Serial No. 690,205, filed on October15, 1957, by Edgar Fischer for Process for the Manufacture ofPolyhalogenated Carboxylic Acids.

The oxidation can be carried out in an acid medium as Well as in analkaline medium. An acid oxidation can, for example, be achieved bymeans of nitric acid while an alkaline oxidation can advantageously beeffected by means of an alkali permanganate. These processes have interalia been described in detail in US. patent application Serial No.452,707, filed on August 27, 1954, by Gerhard Bier, Hans Helmut Frey andKarl Heinz Kahrs for Method for the Preparation of Fuorinated CarboxylicAcids. in both cases it is, however, always mixtures of acids andunreacted unsaturated or saturated starting materials that are obtained.As is known, the separation of these mixtures and the purification ofthe crude polyhalogenated carboxylic acids involve great difficultieswhich are due, on the one hand, to the excellent emulsifying propertiesof these carboxylic acids which properties become apparent above all inan alkaline medium but also in an acid medium and, on the other hand, tothe abnormal solubilities occurring in this class of substances.

Many metallic and non-metallic salts of these acids possess a pronouncedgood solubility in organic media. When the acids are separated fromneutral substances by means of the alkali metal salts, a customaryprocess in organic chemistry, obstinate emulsions form which can bebroken by the addition of neutral salt solutions and, if necessary, bysubjecting them, in addition thereto, to a centrifugation. By theaddition of concentrated hydrochloric acid or the introduction ofgaseous hydrogen "'"o i*"- i 'h uc us salt solution the crude poly-Patented Sept. 15, 1959 ice halogenated carboxylic acids can beprecipitated and sep arated as liquid heavy phase.

The impurities which are still contained in the crude acids at thispoint of the process are mainly alkali metal salts and water. Theworking up by vacuum distillation involves considerable diiliculties.One reason for these difficulties lies in the presence of alkali metalsalts which even in themselves strongly impede a vacuum distillation andwhich at an elevated temperature cause a decomposition of the acids intoolefins, CO and alkali halide. Nor can a vacuum distillation be carriedout when the crude acids have carbon chains of more than 10 to 12 carbonatoms. To work up these products by distillation and to purify them ithas hitherto been necessary to make use of the chlorides or of theesters of these acids with low molecular alcohols which have a muchlower boiling point and which can be distilled more easily. These acidderivatives can moreover be subjected to higher temperatures in vacuowithout any decomposition taking place.

Now I have found that the free acids, preferably those having carbonchains of 4 to 14 carbon atoms, which mainly contain fluorine and whichmay besides contain a second halogen atom such as chlorine or bromineand preferably chlorine, can also be distilled with superheated steam attemperatures of generally more than C. without decomposition takingplace if the distillation is carried out in the presence of at least onehydrogen halide such as hydrogen chloride or hydrogen bromide,preferably hydrogen chloride. The process of this invention does notrequire the application of a vacuum but can be carried out under normalpressure in a simple apparatus. Even when applying steam of more than200 C. no phenomena of decomposition can be observed. In this processthe addition of hydrogen halides and preferably hydrogen chloride has adouble function. Firstly, it serves to prevent the formation of anemulsion ordinarily taking place in the condensate owing to theinteraction of acids and water and secondly it considerably reduces thesolubility in water, particularly that of the low molecularperhalogenated acids.

The hydrogen halide, preferably hydrogen chloride may be introduced intothe distilling vessel, the cooling system or the collecting vessel inthe form of an aqueous solution or in the gaseous state orsimultaneously in the form of an aqueous solution and in the gaseousstate. It is most advantageous to introduce it into a cooling systemwhereby the formation of an emulsion is successfully suppressed in thenascent state already.

The polyhalogenated carboxylic acids purified accord ing to the presentinvention may be used, for example, as emulsifiers.

The following examples as well as the accompanying drawing serve toillustrate the invention without limiting it thereto, the parts being byweight.

Example 1 1000 parts of crude chlorofiuorocarboxylic acids obtained byprecipitating an alkali metal salt solution of chlorofluorocarboxylicacids with concentrated hydrochloric acid and by separating the lowerliquid phase, the said fiuorinated carboxylic acids having been preparedaccording to Example 1 of U.S. patent application Serial No. 690,205,filed on October 15, 1957, by Edgar Fischer for Process for theManufacture of Polyhalogenated Carboxylic Acids and consisting of 94% byWeight of chlorofluorocarboxylic acids having an average equivalentweight of 576, are added dropwise from stock vessel V into distiller Bheated to to 180 C. At the same time steam of 180 C. coming fromsuperheater U is introduced into distiller B. The introduction of thecrude acid is regulated so that there are only about 100 parts ofproduct in distiller B at a time. The acid passing over together withthe steam is condensed in condenser K. At 2 gaseous hydrogen chloride isintroduced into the cooling system in such a quantity that the aqueoushydrochloric acid which forms contains 5 to 10% of hydrogen chloride. Inseparating vessel D the distilled chlorofluorocarboxylic acid separatesas heavier phase and leaves at 4. The aqueous hydrochloric acid flowsoff via tube 3. The distillation with superheated steam is continued aslong as chlorofluorocarboxylic acid passes over. 932 parts of distilledchlorofluorocarboxylic acid having an average equivalent weight of 568and containing a residue on ignition of less than 0.05% by weight areobtained. The accompanying salts which have not been distilled (18parts) remain in distiller B.

Example 2 When introducing gaseous hydrogen bromide instead of gaseoushydrogen chloride into the cooling system and when otherwise proceedingas described in Example 1, the distilled chlorofluorocarboxylic acid hasa faint yellow shade which is caused by small quantities of freehalogen. The latter can easily be eliminated in known manner, forexample by passing through an inert gas. The yield amounts to 918 parts.

I claim:

1. A process for purifying polyhalogenated aliphatic carboxylic acidswith 4 to 14 carbon atoms selected from the group consisting offluorine-containing acids and of acids containing fluorine and a minoramount relative to fluorine of at least one halogen selected from thegroup consisting of chlorine and bromine, which comprises distilling thecrude acid with superheated steam at temperatures of generally more than100 C., at least one hydrogen halide selected from the group consistingof hydrogen chloride and hydrogen bromide being introduced into thedistilling apparatus in the gaseous state simultane- 4 ously with thesteam, whereby decomposition of the fluorine-containing acid is avoided.

2. A process for purifying polyhalogenated aliphatic carboxylic acidswith 4 to 14 carbon atoms selected from the group consisting offluorine-containing acids and of acids containing fluorine and a minoramount relative to fluorine of at least one halogen selected from thegroup consisting of chlorine and bromine, which comprises distilling thecrude acid with superheated steam at a temperature of generally morethan 100 C., at least one hydrogen halide selected from the groupconsisting of hydrogen chloride and hydrogen bromide being introducedinto the distilling apparatus in the form of an aqueous solutionsimultaneously with the steam, whereby decomposition of thefluorine-containing acid is avoided.

3. A process for purifying polyhalogenated aliphatic carboxylic acidswith 4 to 14 carbon atoms selected from the group consisting offluorine-containing acids and of acids containing fluorine and a minoramount relative to fluorine of at least one halogen selected from thegroup consisting of chlorine and bromine, which comprises distilling thecrude acid with superheated steam at a temperature of generally morethan 100 C., at least one hydrogen halide selected from the groupconsisting of hydrogen chloride and hydrogen bromide being introducedinto the distilling apparatus in the form of an aqueous solution and inthe gaseous state simultaneously with the steam, whereby decompositionof the fluorine-containing acid is avoided.

4. A process as claimed in claim 1, wherein hydrogen chloride isintroduced.

5. A process as claimed in claim 1, wherein a carboxylic acid containingchemically bound fluorine and chlorine is purified.

6. Acids whenever purified by the process as claimed in claim 1.

No references cited.

1. A PROCESS FOR PURIFYING POLYHALOGENATED ALIPHATIC CARBOXYLIC ACIDSWITH 4 TO 14 CARBON ATOMS SELECTED FROM THE GROUP CONSISTING OFFLUORINE-CONTAINING ACIDS AND OF ACIDS CONTAINIGN FLUORINE AND A MONORAMOUNT RELATIVE TO FLUORINE OF AT LEAST ONE HALOGEN SELECTED FROM THEGROUP CONSISTING OF CHLORINE AND BROMINE, WHICH COMPRISES DISTILLING THECRUDE ACID WITH SUPERHEATED STEAM AT EMPERATURES OF GENERALLY MORE THAN100* C., AT LEAST ONE HYDROGEN HALIDE SELECTED FROM THE GROUP CONSISTINGOF HYDROGEN CHLORIDE AND HYDROGEN BROMIDE BEING INTRODUCED INTO THEDISTILLING APPARATUS IN THE GASEOUS STATE SIMULTANEOUSLY WITH THE STEAM,WHEREBY DECOMPOSITION OF THE FLUORINE-CONTAINING ACID IS AVOIDED.